Retinal imaging with a confocal scanning laser Ophthalmoscope (cSLO) involves scanning a small laser beam over the retina and constructing an image from the reflected light. By applying the confocal principle, tomographic images can be produced by measuring a sequence of slices at different retinal depths. However, the thickness of such slices, when compared with the retinal thickness, is too large to give useful 3D retinal images, if no processing is done. In this work, a prototype cSLO was modified in terms hardware and software to give the ability of doing the tomographic measurements with the maximum theoretical axial resolution possible. A model eye was built to test the performance of the system. A novel algorithm has been developed which fits a double Gaussian curve to the axial intensity profiles generated from a stack of images slices. The underlying assumption is that the laser light has mainly been reflected by two structures in the retina, the internal limiting membrane and the retinal pigment epithelium. From the fitted curve topographic images and novel thickness images of the retina can be generated. Deconvolution algorithms have also been developed to improve the axial resolution of the system, using a theoretically predicted cSLO point spread function. The technique was evaluated using measurements made on a model eye, four normal eyes and seven eyes containing retinal pathology. The reproducibility, accuracy and physiological measurements obtained, were compared with available published data, and showed good agreement. The difference in the measurements when using a double rather than a single Gaussian model was also analysed.

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In this dissertation, I investigated some fundamental issues related to medical image segmentation, registration, and watermarking. I used color retinal fundus images to perform my study because of the rich representation of different objects (blood vessels, microaneurysms, hemorrhages, exudates, etc.) that are pathologically important and have close resemblance in shapes and colors. To attack this complex subject, I developed a divide-and-conquer strategy to address related issues step-by-step and to optimize the parameters of different algorithm steps. Most, if not all, objects in our discussion are related. The algorithms for detection, registration, and protection of different objects need to consider how to differentiate the foreground from the background and be able to correctly characterize the features of the image objects and their geometric properties. To address these problems, I characterized the shapes of blood vessels in retinal images and proposed the algorithms to extract the features of blood vessels. A tracing algorithm was developed for the detection of blood vessels along the vascular network. Due to the noise interference and various image qualities, the robust segmentation techniques were used for the accurate characterization of the objects’ shapes and verification. Based on the segmentation results, a registration algorithm was developed, which uses the bifurcation and cross-over points of blood vessels to establish the correspondence between the images and derive the transformation that aligns the images. A Region-of-Interest (ROI) based watermarking scheme was proposed for image authenticity. It uses linear segments extracted from the image as reference locations for embedding and detecting watermark. Global and locally-randomized synchronization schemes were proposed for bit-sequence synchronization of a watermark. The scheme is robust against common image processing and geometric distortions (rotation and scaling), and it can detect alternations such as moving or removing of the image content.

INTRODUCTION: Optical coherence tomography (OCT) is used to study retinal structure in schizophrenia. Changes in retinal structure, especially the retinal nerve fiber layer (RNFL) have been correlated with psychotic disorders. Along with a decrease in macular outer nuclear layer (ONL) thickness and an increase in macular outer plexiform layer (OPL). However, measurement variability is a concern for inner retinal layers since there are various generations of OCT devices resulting in differing measurements. We investigated the inter- and intra-device agreement of macular thickness between spectral domain (SD-OCT) and swept source-OCT (SS-OCT), and compared macula and peripapillary group differences in schizophrenia using SS-OCT for inner retinal layers. Additionally, we expanded on our previous work and investigated whether baseline outer retinal layer data for macular ONL and OPL thickness predicted clinical and cognitive changes in individuals with schizophrenia. METHODS: For the inter- and intra-scanner study, macular OCT thickness was obtained for schizophrenia (SZ, n=30) and healthy controls (HC, n= 22) subjects using SD-OCT (Heidelberg Spectralis) and SS-OCT (DRI Topcon Triton). Peripapillary thickness was obtained using SS-OCT. RNFL, ganglion cell-inner plexiform complex (GCL+), RNFL+ GCL+ (GCL++), and macular thickness were collected. For the longitudinal study, 7 participants diagnosed with either schizophrenia or schizoaffective baseline OCT measurements and clinical measures were obtained for all 7 participants from study 1, along with 6 months follow up clinical measures. OCT measurements for the macular OPL and ONL were gathered using the Heidelberg Spectralis Clinical and cognitive data was gathered. All statistical analyses were performed using R software. RESULTS: There was excellent inter-scanner agreement for GCL+ and GCL++ with Interclass correlation coefficient (ICC) values between r =0.92-0.99. Good to excellent intra-scanner agreement was present except for macular RNFL in the SS-OCT device. No significant peripapillary group differences were identified. Poorer (Global Assessment of Functioning) GAF scores were correlated with thinner macular layers. Greater mania symptoms were associated with smaller peripapillary GCL+ thickness (r=-0.43, p=0.03). Poor overall cognition was associated with smaller peripapillary retinal thickness (r=0.36, p=0.02). For the longitudinal study, an increase in baseline OPL thickness was correlated with worse positive symptoms according to the Positive and Negative Symptom Severity(PANSS) at the 6 month follow up (r=0.77, p=0.04) with a trend level effect for PANSS total scores (r=0.71, p=0.08). There was no significant correlation between the change in clinical or cognitive outcomes for 6 months and baseline OPL and ONL thickness. CONCLUSION: While there is RNFL variability, GCL+ and GCL++ are comparable between scanners SD-OCT and SS-OCT. Given that RNFL thinning is strongly implicated in psychotic disorders, the use of OCT scanners should not be interchanged due to increased RNFL measurement variability. Additionally, though further research is needed on investigating changes in clinical outcomes with changes in OCT measurements, OPL thickness might be a predictor of long-term clinical outcomes or changes in brain pathology for individuals with schizophrenia.

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Purpose: The RTVue-100 is a new instrument for measuring retinal blood flow (RBF), but image quality needs to be optimized in order for valid blood flow results. The primary aim of this thesis was to assess the presence of learning effects with novice and experienced operators. Methods: Twelve upper-year optometric students from the University of Waterloo, School of Optometry and Vision Science, were trained in operating RTVue-100. Nine healthy participants, with a mean age (?? SD) of 25.7 ?? 3.8 years, underwent OCT imaging. Using the Doppler OCT of Retinal Circulation (DOCTORC) software, images were assessed by computer for various image quality parameters. Results: Paired samples t-tests showed significant statistical differences between the novice and experienced operators for the following image acquisition parameters: total acquisition time (TAT), number of attempts to complete total scan protocol, and number of valid images. Mean values for TAT and the number of attempts decreased, whereas the mean number of valid images increased from novice to experienced level. Conclusions: The results confirm that there are learning effects observed within the image acquisition process using the RTVue-100 SD-OCT.

A fundus camera a complex optical system that makes use of the principle of reflex free indirect ophthalmoscopy to image the retina. Despite being in existence as early as 1900's, little has changed in the design of a fundus camera and there is minimal information about the design principles utilized. Parameters and specifications involved in the design of fundus camera are determined and their affect on system performance are discussed. Fundus cameras incorporating different design methods are modeled and a performance evaluation based on design parameters is used to determine the effectiveness of each design strategy. By determining the design principles involved in the fundus camera, new cameras can be designed to include specific imaging modalities such as optical coherence tomography, imaging spectroscopy and imaging polarimetry to gather additional information about properties and structure of the retina. Design principles utilized to incorporate such modalities into fundus camera systems are discussed. Design, implementation and testing of a snapshot polarimeter fundus camera are demonstrated.

Approved for public release; distribution is unlimited / The connection between eye disease and diabetes is proven and is no longer a point of conjecture. In focusing attention on the retina, profound inroads have been made in the fight against this dreaded disorder of the blood. By carefully imaging the blood vessels in the eye, medical professionals can make accurate diagnoses based upon the changes and abnormalities observed. In addition, because the vasculature in the retina is extremely sensitive to fluctuations in normal bodily processes, often the first indication of diabetes and many other diseases manifest themselves here and are found during routine eye examinations. This thesis will explore the possibilities of a new method of retinal imaging by the blending and application of existing technologies. With the use of an automated, infrared-based imaging system, problems related to human error and the limitations of existing methods can be readily resolved and the groundwork can be laid for a new standard of accuracy in retinal imaging. Most importantly, it will automate the entire procedure providing medical specialists heretofore unavailable accuracy in their diagnoses. / http://archive.org/details/functionalspecif00domb / Lieutenant, United States Navy

abstract: There is a robust association between psychosis and cannabis use, but the mechanisms underlying this relation are poorly understood. Because both psychosis and cannabis use have been linked to cardiovascular problems, it is possible that cannabis use exacerbates an underlying vascular vulnerability in individuals prone to psychosis. To investigate microvascular differences in individuals with psychotic symptoms and cannabis use, the current study tested associations between psychotic-like experiences, cannabis use, and retinal vessel diameter in 101 young adults (mean age=19.37 years [SD=1.93]). Retinal venular diameter did not differ between participants with (M=218.08, SD=15.09) and without psychotic-like experiences (M=216.61, SD=16.18) (F(1, 97)=0.01, p=.93) or between cannabis users (M=218.41, SD=14.31) and non-users (M=216.95, SD=16.26) (F(1, 97)=0.37, p=.54). Likewise, mean retinal arteriolar diameter did not differ between participants with (M=157.07, SD=10.96) and without psychotic-like experiences (M=154.88, SD=9.03) (F(1, 97)=0.00, p=.97). However, cannabis users had statistically significantly wider retinal arterioles (M=159.10, SD=9.94) than did non-users (M=154.29, SD=10.20) (F(1, 97)=5.99, p=.016), and this effect was robust to control for covariates. There was no evidence of an interaction between psychotic-like experiences and cannabis use in predicting retinal vessel diameter. These results indicate that cannabis use is associated with microvascular differences in young adulthood. Given current trends toward legalization of recreational cannabis use, future research should explore these differences and their potential consequences for cardiovascular health. / Dissertation/Thesis / Masters Thesis Psychology 2016